rotary mechanism

ABSTRACT

A rotary mechanism including a rotor assembly having a plurality of piston members distributed about its periphery, and a rotary member in peripheral engagement with the rotor assembly. The rotary member ( 7 ) includes a plurality of piston receiving formations in its periphery for receiving the piston members, whereby during rotation of the rotor assembly the piston members move into and out of the piston receiving formations, and a plurality of conduits arranged to connect peripheral portions of the rotary member to an interior portion thereof. The rotary mechanism includes a flow separation device having an inlet port for receiving fluid into the rotary mechanism and an outlet port for enabling fluid to exit the rotary mechanism, a first passageway for connecting the inlet port with the interior side of at least one of the conduits formed in the rotary member and a second passageway for connecting the outlet port with the interior side of at least one of the conduits formed in the rotary member.

The invention relates to a rotary mechanism, such as a pump, for propelling fluid. The rotary mechanism can also be driven by the fluid and in this arrangement acts as a motor.

There are many types of pump that are known in the art, for example, centrifugal, impeller, piston and gerotor pumps. Another common type of pump is a gear pump. A gear pump typically includes two spur gears located in a casing having an inlet and an outlet. As the gears rotate they separate on the intake side of the pump creating a void and suction, which draws fluid into the casing. Fluid is carried from the inlet by the gear teeth to the outlet where the fluid is discharged by the meshing of the gear teeth. Gear pumps have very tight tolerances and high operational speeds to prevent fluid from leaking back to the inlet side of the pump.

An example of a gear pump is disclosed in GB381,148. That pump includes upper and lower meshed gear elements, wherein the lower gear element includes an arrangement of bores that connect the outer extremity of the gear teeth and the troughs formed between the teeth to the interior of the gear wheel. The pump also includes an adjustable valve member in the interior of the gear wheel. Fluid is fed to the gear pump from a tangentially arranged fluid inlet port and exits the pump via a tangentially arranged fluid output port.

The arrangement is such that fluid from the high pressure side of the pump can enter the radial passages to enter the interior of the gear member and the adjustable valve member is arranged to redirect the fluid, for example to the low pressure side of the pump. The purpose of this device is to enable fluid trapped between the meshing teeth to be returned to the low pressure side of the pump without heating the fluid by compression, which normally occurs when the radial passageways are not provided in a standard gear pump. Alternatively, the trapped fluid can be directed to a secondary circuit, however this provides a very limited feed since the quantity of fluid trapped between the gear teeth is small. This is in part because the gear teeth are of the involute type, which does not provide a well sealed meshing arrangement. Although the direction of flow of fluid entering the gear pump is substantially tangential to the gear wheels, it is in a direction that is opposite to the direction of rotation of the gear wheels. This is not an optimised arrangement.

Accordingly, the invention seeks to provide a new type of pump/and or motor device that to mitigate at least one of the aforementioned problems, or to at least provide an alternative arrangement to known pumps.

According to a first aspect of the invention there is provided a rotary mechanism arranged to propel fluid, such as a pump, and/or to be driven by a fluid, such as a motor, said rotary mechanism including: a rotor assembly having a plurality of piston members distributed about its periphery; a rotary member in peripheral engagement with the rotor assembly, said rotary member having a plurality of piston receiving formations in its periphery for receiving the piston members, the arrangement being such that during rotation of the rotor assembly the piston members move into and out of the piston receiving formations, and a plurality of conduits arranged to connect peripheral portions of the rotary member to an interior portion thereof; a flow separation device including an inlet port for receiving fluid into the rotary mechanism and an outlet port for enabling fluid to exit the rotary mechanism, a first passageway for connecting the inlet port with the interior side of at least one of the conduits formed in the rotary member and a second passageway for connecting the outlet port with the interior side of at least one of the conduits formed in the rotary member wherein the arrangement is such that, in use, the action of withdrawing the piston members from the piston receiving formations draws fluid into the rotary mechanism from the fluid inlet; and wherein the rotary member is rotatable relative to the flow separation device and at least some of the rotary member conduits periodically align with the first and second passageways formed in the flow separation device thereby enabling the fluid received from the inlet to flow outwards towards a first peripheral portion of the rotary member, wherein it is transported to a second peripheral portion of the rotary member by the rotor assembly, and for the fluid to flow away from the second peripheral portion of the rotary member to the outlet port, wherein the flow separation device is constructed and arranged to separate the incoming and outgoing flows.

The invention provides a significant advantage over gear pumps because each of the pistons propels a relatively large volume of fluid into the piston receiving formations, which provides a large throughput of fluid. Since the inlet and outlet ports are formed in the flow separation device the arrangement allows for the inlet and outlet to be arranged substantially axially with respect to the rotary member.

The primary inlet and outlet flows pass through the rotary member and the separation device.

Advantageously the input port can be arranged substantially parallel to the axis of the rotary member and/or rotor assembly. Advantageously the first passage way formed in the flow separation device is constructed and arranged to redirect the incoming flow of fluid through approximately 90 degrees. The flow changes from a substantially axial direction to a substantially radial direction. The flow separation device includes a substantially cylindrical body and the input port is located in an end face thereof and the first passage way is arranged to redirect the incoming flow through the body to exit substantially radially at a first aperture formed in the curved surface of the substantially cylindrical body. Preferably the first aperture formed in the curved surface of the body is sized to simultaneously align with a plurality of conduits formed in the rotary member, and more preferably still to simultaneously align with n conduits, wherein n is in the range two to four conduits. Advantageously the orientation of the separation device is fixed. The rotary member is mounted thereon and is arranged to rotate about the separation device.

Advantageously the output port can be arranged substantially parallel to the axis of the rotary member and/or rotor assembly. Advantageously the second passage way formed in the flow separation device is constructed and arranged to redirect the outgoing flow of fluid through approximately 90 degrees. The flow changes from a substantially radial direction to a substantially axial direction. The output port can be located in either of the end faces of the substantially cylindrical body, but preferably is located in the same end face as the input port. The second passageway includes a second aperture formed in the curved surface of the substantially cylindrical body and directs the outgoing flow to the outlet port. Preferably the second aperture formed in the curved surface of the body is sized to simultaneously align with a plurality of conduits formed in the rotary member, and more preferably still to simultaneously align with n conduits in the range two to four conduits.

Advantageously the flow separation device can be arranged to direct the incoming fluid towards the rotor assembly such that the incoming fluid impinges on the rotor assembly in a substantially tangential direction in the direction of rotation of the rotor assembly.

The piston receiving formations are preferably substantially U-shaped slots. The U-shaped slots are formed in the periphery of the rotary member with the open part facing radially outwards. The piston receiving formations include at least one pair of substantially parallel sides. Preferably the fit between the recess side walls and the piston member is tight, with the clearance being typically in the range 0.01 to 0.03 mm.

Advantageously the piston receiving formations are evenly distributed about the periphery of the rotary mechanism. Each adjacent pair of piston receiving formations is separated by a radially extending protrusion. Advantageously each piston receiving formation is connected with the interior of the annular rotary member by at least one conduit. Advantageously each radially extending protrusion is connected with the interior of the annular rotary member by at least one conduit. Preferably each conduit is substantially rectilinear and is arranged along a substantially radial path. Preferably each conduit has a substantially circular cross-section. The action of withdrawing the piston members from the piston receiving formations draws fluid into the rotary mechanism from the fluid inlet, along the first passageway into at least one of the conduits formed in the rotary member thereby filling the piston receiving formation and flowing outwards into the low pressure side of the mechanism for transportation by the rotor assembly to the high pressure side. The action of the piston members moving towards and into the piston receiving formations forces the outgoing fluid through the conduits, into the second passageway and to exit the rotary mechanism via the outlet port.

The rotary mechanism includes a casing assembly for housing the rotor assembly, the rotary member and the flow separation device. Advantageously the casing assembly includes a part having an inner profile that substantially matches the plan of the outer profiles of the rotor assembly and the rotary member, thus providing an inner profile similar to the outer profile of the numeral “8”. The inner profile sets a boundary thereby restricting the radial flow of the fluid. The casing includes front and rear covers, which prevent fluid flowing axially out of the piston receiving formations. The part of the casing that includes the inner profile preferably includes at least first and second parts that can be separated from each other in order to enable the rotor assembly to be mounted therein.

Each piston member comprises a body having a substantially cylindrical or substantially spherical portion. Having cylindrical members is particularly advantageous since it provides a structurally simple arrangement and also allows for a very small clearance between the piston members and the inner periphery of the casing, which is typically approximately 0.000035 to 0.0001 mm. The rotor assembly described is different from the involute gears used in gear pumps.

Advantageously the geometry of the piston members and the piston receiving formations can be such that interaction between pistons and the piston receiving formations periodically accelerates and decelerates the rotary member. This leads to a non-constant speed of rotation thereby producing a pulsed output. This can be achieved, for example by having piston members that each include a substantially cylindrical part and piston receiving formations that are each substantially U-shaped and have substantially parallel sides.

The nominal ratio between the number of piston members and the number of piston receiving formations is typically in the range 4:1 to 1:4, but is not restricted to these ranges. The rotor assembly can include n piston members, wherein n is in the range 1 to 20, preferably 2 to 15 and more preferably still 3 to 12. The rotor assembly can include any practicable number of piston members.

The rotor assembly can include a support member for supporting each of the piston members, the arrangement being such that the piston members are located about the periphery of the support member and are arranged to rotate with the support member about a first axis, wherein at least one of the piston members is arranged to rotate relative to the support member about a second axis. Preferably the second axis is the longitudinal axis of the piston member, which enables the piston members to wear more evenly. Advantageously the first axis is substantially parallel to the second axis. Advantageously each piston is arranged to rotate relative to the support member about its own axis, wherein each piston axis is arranged substantially parallel to the first axis.

Advantageously the rotary mechanism can include a plurality of rotor assemblies in peripheral engagement with the rotary member. Advantageously each rotor assembly can be configured according to any configuration of rotor assembly described herein. Advantageously the rotary mechanism can include any practicable number of rotor assemblies. Preferably the rotary mechanism includes n rotor assemblies in peripheral engagement with the rotary member, wherein n is in the range 2 to 10, preferably in the range 2 to 6, and more preferably still in the range 2 to 4.

The flow separation device can include a plurality of inlet ports and/or a plurality of outlet ports. Advantageously the flow separation device can include an inlet port and an outlet port for each rotor assembly. This enables each rotor assembly to serve separate fluid circuits and/or to combine at least some of the outlet flows into a single fluid circuit. In this arrangement, the flow separation device includes separate passageways for connecting each inlet and each outlet port to the conduits. Advantageously each inlet and outlet port can be similarly arranged to those described above. Advantageously at least one of the inlet and outlet ports can be connected to at least one passageway in the separation device that has at least first and second outlets for connecting with the conduits. For example, the flow separation device can be arranged to include a single inlet port, a plurality of inlet apertures formed in the curved surface of the substantially cylindrical body, preferably one for each rotor assembly, and an inlet passageway connecting each of the inlet apertures to the inlet port; and/or a single outlet port, a plurality of outlet apertures formed in the curved surface of the substantially cylindrical body, preferably one for each rotor assembly, and an outlet passageway connecting each of the outlet apertures to the outlet port.

Advantageously the rotary mechanism can include a gear set for synchronising the rotation of the or each rotor assembly and the rotary member. The gear set can include a first gear pair comprising first and second gear elements, wherein each of said first and second gear elements includes meshing zones and non-meshing zones formed in its periphery and the first gear element is arranged to rotate with the second gear element; and a second gear pair including third and fourth gear elements, wherein each of the third and fourth gears elements includes a plurality of meshing zones and non-meshing zones formed in its periphery and the third gear element is arranged to rotate with the fourth gear element; wherein the first and second gear pairs are in meshing engagement such that the first gear element meshes with the third gear element and the second gear element meshes with the fourth gear element, and drive between the first and second gear pairs is transmitted alternately between the first and third gears and the second and fourth gears.

A gear set arranged in this manner enables the generation of peak acceleration curves having no dwell and an abrupt reversal of acceleration. Advantageously the first gear pair can be coupled to the rotor assembly and the second gear pair can be coupled to the rotary member. This type of gear set is used to synchronise the rotor assembly and the rotary member wherein the geometry is such that it provides pulsed rotation, that is, where acceleration and deceleration occur during a full rotation.

For each of the first and second gear elements, the non-meshing zones are arranged alternately with the meshing zones, the first and second gear elements are arranged substantially co-axially such that the meshing zones of the first gear element are rotationally offset from the meshing zones of the second gear element. Each of the first and second gear elements can include a central portion and a plurality of lobes distributed around the periphery of the central portion, wherein each lobe includes a peripheral portion having meshing means formed therein. Advantageously the periphery of each lobe is substantially part elliptical.

For each of the third and fourth gear elements the non-meshing zones are arranged alternately with the meshing zones, the third and fourth gear elements are arranged substantially co-axially such that the meshing zones of the third gear element are rotationally offset from the meshing zones of the fourth gear element. Each of the third and fourth gear elements includes concave portions formed in its periphery, wherein alternate concave portions including meshing means formed therein. Advantageously the concave portions are substantially part elliptical.

Typically the meshing means includes involute gear teeth.

Advantageously the gear set can be arranged such that the minimum speed occurs at the handover of meshing engagement from at least one of the first and third gear elements to the second and fourth gear elements and from the second and fourth gear elements to the first and third gear elements; and/or the maximum speed occurs when either the first or second gear element pair are fully engaged.

Advantageously the first and second gear pairs are arranged such that the second gear element meshes with the fourth gear element before the first gear element fully disengages the third gear element. Advantageously the first and second gear pairs are arranged such that the first gear element meshes with the third gear element before the second gear element fully disengages the fourth gear element.

According to another aspect of the invention there is provided a pump and/or a motor including a rotor assembly having a plurality of piston members distributed about its periphery and a rotary member in peripheral engagement with the rotor assembly, said rotary member including a plurality of formations in its periphery for receiving the piston members, the arrangement being such that during rotation of the rotor assembly and rotary member the piston members move into and out the piston receiving formations. Each piston comprises a body having a substantially cylindrical or substantially spherical portion. Thus the rotor assembly described has a different structure to the gears used in gear pumps.

Advantageously the rotary member according to the second aspect of the invention can be arranged in accordance with any configuration described herein of the first aspect of the invention.

The rotor assembly includes a support member for supporting each of the piston members, the arrangement being such that the piston members are arranged to rotate with the support member about a first axis, wherein at least one of the pistons is arranged to rotate relative to the support member about a second axis. Advantageously the first axis is substantially parallel to the second axis. Advantageously each piston is arranged to rotate relative to the support member about its own axis, wherein each piston axis is arranged substantially parallel to the first axis.

Advantageously the rotary member can be a valve member that is arranged to block fluid flowing from a high pressure side to a low pressure side.

Advantageously the rotor assembly can be arranged such that it only periodically engages the rotary member during a full 360 revolution. This enables the rotor assembly to move the valve to a blocking position, wherein the interaction of the rotary assembly and rotary member blocks the flow of fluid from the high pressure side to the low pressure side, so that the next piston member can drive the fluid out of the pump via the outlet. The piston member then engages the rotary member and rotates it through a predetermined angle as the piston member moves to the low pressure side of the pump, thereby resetting the valve member to another blocking orientation to prevent fluid being driven by the next piston member from crossing to the inlet side.

Advantageously the rotary mechanism can include a gear set for synchronising the rotation of the rotor assembly and the rotary member. Advantageously the rotor assembly and the rotary member can be arranged such that they rotate at substantially constant speed throughout a full 360 revolution for any given nominal speed. In this arrangement, the gear set can include standard gears for synchronising rotation. The gear set ensures that the rotary member is continuously rotated when the rotor assembly rotates even when the rotor assembly is not in engagement with the rotary member.

Advantageously the input and output ports can be arranged substantially parallel to the axis of the rotor assembly and/or the rotary member. Alternatively, the input and output ports can be arranged substantially radial or tangential to the rotor assembly.

According to another aspect of the invention there is provided a gear set for synchronising the rotation of first and second rotary members, said gear set including, a first gear pair comprising first and second gear elements, wherein each of said first and second gear elements includes meshing zones and non-meshing zones formed in its periphery and the first gear element is arranged to rotate with the second gear element; and a second gear pair including third and fourth gear elements, wherein each of the third and fourth gears elements includes a plurality of meshing zones and non-meshing zones formed in its periphery and the third gear element is arranged to rotate with the fourth gear element; wherein the first and second gear pairs are in meshing engagement such that the first gear element meshes with the third gear element and the second gear element meshes with the fourth gear element, and drive between the first and second gear pairs is transmitted alternately between the first and third gears and the second and fourth gears. The gear set enables the generation of peak acceleration curves having no dwell and an abrupt reversal of acceleration. Therefore the gear set can be used to synchronise first and second rotary members that are in meshing engagement for at least part of a full revolution wherein the geometry is such that each member does not rotate at a constant speed through a full revolution. Thus the gears can provide synchronisation of the rotor assembly and the rotary member in the rotary mechanism described herein. Having a double gear arrangement provides a strong structure.

Advantageously the first gear pair can be coupled to the rotor assembly and the second gear pair can be coupled to the rotary member. This type of gear set is used to synchronise the rotor assembly and the rotary member wherein the geometry is such that it provides pulsed rotation, that there is acceleration and deceleration during a full rotation.

For each of the first and second gear elements, the non-meshing zones are arranged alternately with the meshing zones, the first and second gear elements are arranged substantially co-axially such that the meshing zones of the first gear element are rotationally offset from the meshing zones of the second gear element. Each of the first and second gear elements can include a central portion and a plurality of lobes distributed around the periphery of the central portion, wherein each lobe includes a peripheral portion having meshing means formed therein. Advantageously the periphery of each lobe is substantially part elliptical.

For each of the third and fourth gear elements the non-meshing zones are arranged alternately with the meshing zones, the third and fourth gear elements are arranged substantially co-axially such that the meshing zones of the third gear element are rotationally offset from the meshing zones of the fourth gear element. Each of the third and fourth gear elements includes concave portions formed in its periphery, wherein alternate concave portions including meshing means formed therein. Advantageously the concave portions are substantially part elliptical.

Typically the meshing means includes involute gear teeth.

Advantageously the gear set can be arranged such the minimum speed occurs at the handover of meshing engagement from at least one of the first and third gear elements to the second and fourth gear elements and from the second and fourth gear elements to the first and third gear elements; and/or the maximum speed occurs when either the first or second gear element pair are fully engaged.

Advantageously the first and second gear pairs are arranged such that the second gear element meshes with the fourth gear element before the first gear element fully disengages the third gear element. Advantageously the first and second gear pairs are arranged such that the first gear element meshes with the third gear element before the second gear element fully disengages the fourth gear element.

According to another aspect of the invention there is provided a gear set for synchronising the rotation of first and second rotary members in a rotary mechanism, said gear set including, a first gear pair comprising first and second gear elements, wherein each of said first and second gear elements includes meshing zones and non-meshing zones formed in its periphery such that the non-meshing zones are arranged alternately with the meshing zones, and wherein the first and second gear elements are arranged substantially co-axially such that the meshing zones of the first gear element are rotationally offset from the meshing zones of the second gear element, and the first gear element is arranged to rotate with the second gear element.

According to another aspect of the invention there is provided a pump and/or motor including a gear set according to any one of the preceding claims.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying Figures, wherein:

FIG. 1 is an isometric view of a pump/motor in accordance with the invention;

FIG. 2 is an isometric view of the pump in FIG. 1, with some of the outer casing members removed thereby revealing a piston rotor assembly, a piston receiving wheel and a flow separation device in the form of a splitter element;

FIG. 3 is an isometric view of part of the piston rotor assembly and the piston receiving wheel;

FIG. 4 is a front view of part of the piston rotor assembly, piston receiving wheel and splitter element;

FIG. 5 is an isometric view of a set of piston elements, the piston receiving wheel and the splitter element;

FIG. 6 is an enlarged isometric view of the splitter element;

FIG. 7 is an enlarged view of an alternative splitter element that includes a seal protruding from a dividing wall;

FIGS. 8 a-8 k are views of optional gear elements for driving and synchronising rotation of the piston rotor and piston receiving wheel;

FIG. 9 is a graph showing the relative speed of the rotor assembly against the rotation angle of a piston, which is the same as the rotation angle of the rotor assembly;

FIG. 10 is an isometric view of a differently constructed piston receiving wheel;

FIG. 11 is an isometric view of part of the piston receiving wheel of FIG. 10;

FIG. 12 is a schematic view of a second embodiment of the invention;

FIG. 13 is a schematic view of a third embodiment of the invention;

FIG. 14 is a schematic view of a fourth embodiment of the invention; and

FIG. 15 is a schematic view of a fifth embodiment of the invention.

FIGS. 1 to 7 show a pump 1, having a casing 3, a piston rotor assembly 5, a piston receiving wheel 7, a fluid inlet 9, a fluid outlet 11, and a splitter element 13. The pump 1 shown can be used to pump many different types of fluids such as hydraulic fluids and water.

The rotor assembly 5 is arranged to transfer fluid from a lower pressure side of the pump to a high pressure side and includes a drive shaft 15, an annular support member 17, two piston carrier plates 19, six piston elements 21, front and rear seals 23 and front and rear bearings 25. The support member 17 and piston carrier plates 19 are keyed to the drive shaft 15 and are arranged for rotation therewith. The piston carrier plates 19 include six through holes 25 that are each arranged to receive one of the piston elements 21. The piston elements 21 are evenly distributed about the support member 17, the arrangement being such that the angles subtended between the centres of two adjacent piston elements 21 is approximately 60° (see angle α in FIG. 4). The piston elements 21 rotate with the drive shaft 15. Rotation of the drive shaft 15 is supported by the bearings 25. Seals 23 prevent leakage of fluid from the pump 1. Optionally, each piston element 21 can be arranged to rotate about its longitudinal axis within its hole 25. The axes are arranged substantially perpendicular to the end faces of the piston elements 21 shown in FIG. 4. This evens out the wear on the piston elements 21 as they rotate within the casing 3.

The rotor assembly 5 is arranged in meshing engagement with the piston receiving wheel 7. The piston receiving wheel 7 includes a substantially annular body having twelve recesses formed in its outer periphery. The recesses 27 are substantially U-shaped in cross section, with each side wall 29 of the recess 27 being substantially parallel to a radial centre line and hence to each other (see FIG. 4). The depth of the U-shaped recess is approximately the same as the diameter of each piston element 21. The recesses 27 are evenly distributed about the periphery of the piston receiving wheel 7 such that the angles subtended between the centre lines of two adjacent recesses is approximately 30° (see angle β in FIG. 4). Located between each adjacent pair of recesses 27 is a peripheral portion 31 of the piston receiving wheel 7. The peripheral portions 31 of the piston receiving wheel are arranged to sealingly engage with the annular support member 17 in the rotary piston assembly 5 thereby preventing the flow of fluid from the output side 59 to the inlet side 61. A first set of passageways 33 connect the interior of the piston receiving wheel with each of the recesses 27. A second set of passageways 35 connect the interior of the piston receiving wheel 7 with the peripheral portions 31 of the piston receiving wheel. The arrangement being such that fluid can be communicated between the interior and exterior of the piston receiving wheel 7 by the passageways 33,35 as explained below.

The piston receiving wheel 7 is mounted on a substantially cylindrical splitter member 13. The splitter member 13 is mounted on pegs (not shown) the arrangement being such that its position is fixed relative to the casing 3. The piston receiving wheel 7 is arranged to rotate freely about the splitter element 13.

The splitter element 13 includes an end face 37 having an inlet opening 9 and an outlet opening 11. The inlet and outlet openings 9,11 extend substantially parallel to the longitudinal axis of the substantially cylindrical splitter element 13 to around 60% of the depth of the splitter element (see FIG. 6). A first slot 39 is formed in the curved surface of the cylindrical splitter element 13 and extends a sufficient depth into the splitter element 13 such that it connects substantially perpendicularly with the inlet opening 9. A second slot 41 is formed in the curved surface 38 that connects substantially perpendicularly with the outlet opening 11. The arrangement of the first and second slots 39,41 are in fluid communication with the passageways 33,35 formed in the piston receiving wheel 7. The arrangement is such that fluid entering the inlet opening 9 turns through approximately 90° and exits the splitter element via the first slot 39 and then flows through the passageways 33,35 to exit the piston receiving wheel 7 into the low pressure side 61 of the pump. Similarly, fluid can be communicated from the high pressure side 59 through the passageways 33,35 through the second slot 41 through an angle of approximately 90° to exit the pump 1 substantially axially via the outlet opening 11. The dividing wall 43 between the first and second apertures 39,41 separates the incoming and outgoing fluids. Optionally, the dividing wall 43 can include a seal member 45 that is arranged to engage with the inner curved surface of the piston receiving wheel 7 (see FIG. 7). The seal 45 can comprise a static seal, or alternatively the splitter element 13 may include a resilient member urging it outwards into engagement with the inner curved surface of the piston receiving wheel 7. Thus as the seal 45 wears, the resilient member (not shown), such as a spring, urges the seal 45 into engagement as the seal wears.

The casing 3 includes a front plate 47, a rear plate 49 and a centre section comprising a lower part 51 and an upper part 53. The upper and lower parts 53,51 are separable in the directions marked A in FIG. 2. They are connected together by dowels 55. The casing is arranged in this manner to enable the rotor assembly 5 to be inserted into the casing 3. The upper and lower parts 53,51 include substantially circular apertures formed therein to accommodate the rotor assembly 5 and the piston receiving wheel 7. The arrangement being such that the rotor assembly 5 and the piston receiving wheel 7 can rotate freely relative to the upper and lower parts of the casing 53,51. The tolerances between the piston elements 21 and inner periphery 57 are tight, typically in the range 0.000035 to 0.0001 mm, to prevent fluid from flowing backwards towards the inlet 9 during operation of the pump 1.

The pump 1 is driven by a drive source (not shown) for example an electric motor. The electric motor drives the drive shaft, and hence the rotor assembly 5, either directly or indirectly, for example via a gear set or a flexible drive system such as a belt drive system. The piston receiving wheel 7 is driven by the rotor assembly 5 as it rotates. When the casing 3 is fully assembled, the recesses 27 are effectively piston chambers and the piston elements 21 move into and out of the piston chambers 27 reciprocally as the rotor assembly 5 rotates through an angle of approximately 60°, with the maximum extent of movement within the piston chamber 27 being reached after approximately 30° of rotation.

In the embodiment shown in FIGS. 1 to 7 the ratio of the number of piston elements 21 to the number of piston receiving formations is 6:12 (1:2). However, the arrangement of the piston elements 21 and the profiles of the recesses 27 does not lead to a constant speed of pumping since the pressure line is not rectilinear but rather is curvilinear, that is the effective pitch circle diameter varies with the angle of engagement and thus the effective ratio changes according to the relative rotational orientations of the rotor assembly 5 and the piston receiving wheel 7. Thus although the piston rotor assembly 5 is driven at a constant speed by the drive source, the interaction of the piston elements and piston chambers 27 provides a cyclic pulsed pumping effect, that is the rotor assembly 5 and piston receiving wheel 7 accelerate and decelerate cyclically according to the interaction between the piston elements 21 and recess profiles 27.

FIG. 9 shows a graph of the relative speed of the rotor assembly 5 versus the rotation angle of a piston 21 on the rotor assembly 5. It can be seen from the graph that the speed of the rotor assembly 5 is not constant as it rotates but rather changes periodically according to the interaction between the pistons 21 and the piston receiving wheel 7. The maximum speed occurs at the piston change over point, that is, when a new piston 21 engages the piston receiving wheel 7 and a current piston 21 is in the process of disengaging the piston receiving wheel. The minimum speed occurs when the currently engaged piston 21 is moved to its maximum extent within the recess 27. In the embodiment shown, the cycle repeats itself every 60 degrees of rotation of the rotor assembly 5.

In order to take account of the change in speed of the rotor assembly 5 the inventor has developed a new gear set that can be used to drive the rotor assembly 5 and the piston receiving wheel 7 synchronously. The gears are optional since the rotation of the rotor assembly 5 and piston receiving wheel 7 is automatically synchronised since there is always at least one piston element 21 in engagement with the piston receiving wheel 7, however they can improve the quality of drive even when not strictly required.

The shape of the gears can be seen in FIGS. 8 a-k. The gear train includes first and second pairs of gears 63,65. The first pair of gears 63 includes first and second gears 67,69. The first gear 67 includes an annular portion 71 and three lobes 73 evenly distributed about the periphery of the annular portion 71 such that the angle subtended between the centre lines of two adjacent lobes 73 is approximately 120°. Located between each lobe 73 is a cutaway portion 75. Each lobe 73 comprises a 60° segment (see angle γ in FIG. 8 a). Each lobe 73 includes spur gear teeth 77 in its periphery having involute profiles. The periphery of each lobe 73 is a segment of an ellipse having an effective radius, and hence a centre point from which the gear teeth are created, that is smaller than the overall radius of the gear. That is the gear teeth 77 are generated from a centre point that falls on the lobe 73, whereas the centre point for the overall first gear 67 is the centre of the annular member 71.

The second gear wheel 69 is similar to the first gear wheel 67. The first gear pair 63 comprises the first and second gears 67,69 arranged coaxially with their lobes rotationally oriented 60° out of phase (see FIGS. 8 b-k). The first and second gears 67,69 of the first gear pair 63 are arranged to rotate with each other, with their relative orientations being fixed.

The second gear wheel pair 65 includes third and fourth gears 79,81. The third gear 79 comprises a substantially annular body that includes twelve concave sides 83 formed in its periphery, thus giving it a modified dodecagon appearance, wherein alternate concave sides 83 include involute spur gear teeth 85. Each concave side 83 follows a part elliptical profile. Each side 83 of the third gear 79 subtends an angle of approximately 30° (see angle θ in FIG. 8 a). At the intersection of the toothed and non-toothed sides 83, are teeth 86 that have an involute form facing its respective toothed side 83 and a rounded form to blend with the non-toothed concave side 83, and thus the teeth 86 are wider than the teeth 85.

The fourth gear 81 is similar to the third gear 79. The second pair of gears 65 comprises the third and fourth gears 79,81 arranged substantially coaxially but orientated 30° out of phase (see FIGS. 8 b-k) such that the toothed sides 83 of the third and fourth gears 79,81 are rotationally offset from each other. The third and fourth gears 79,81 of the second gear pair 65 are arranged to rotate with each other, with their relative orientations being fixed.

When the pump 1 uses the first and second gear pairs 63,65 to synchronise the rotation of the rotor assembly 5 and piston receiving wheel 7, the first gear pair 63 is coupled to the drive shaft 15 and the second gear pair 65 is coupled to the piston receiving wheel 7, the arrangement being such that the first and second gear pair 63,65 are in mesh (see FIGS. 8 b-k). The nominal gear ratio is 1:2 to match the nominal ratio of the rotor assembly 5 and piston receiving wheel 7. However, the arrangement of the gear set 63,65 provides variation in the actual ratio as the gears rotate. In the example shown, the ratio varies between 1:1.49 to 1:2.41, though it should be appreciated by the skilled person that the acceleration curve can be usefully adapted to many other periods of acceleration, centre of distances and nominal gear ratio, where peak curves are encountered. The orientation of the gears relative to the rotor assembly 5 and the piston receiving wheel 7 are carefully orientated to ensure that the instantaneous gear ratio is properly matched to the speed profile of the rotor assemblies. The meshing arrangement is such that the gear teeth 77 of the first gear 67 mesh with the teeth 85 of the third gear 79 and the teeth 77 of the second gear 69 mesh with the teeth 85 of the fourth gear 81, wherein there is a handover of drive from the first and third gears to the second and fourth gears 69,81, and vice versa, every 60° of rotation of the first gear pair 63 and every 30° of rotation of the second gear pair 65 (see FIGS. 8 b-8 k).

FIGS. 8 b-c show first and third gears 67,79 engaging and the third and fourth gears 69,81 disengaging. FIGS. 8 d-e show the first and third gears 67,79 fully engaged and the third and fourth gears 69,81 fully disengaged. FIGS. 8 f-g show the first and third gears 67,79 disengaging and FIGS. 8 h-i show the second and fourth gears 69,81 engaging. FIGS. 8 j-k show the second and fourth gears 69,81 fully engaged and the first and third gears 67,79 fully disengaged. The slowest speed occurs at each gear handover when one of the lobed gears 67,69 engages and the other disengages its respective third and fourth gear 79,81. The gear handover takes place smoothly. The fastest speed occurs when either of the first and second gears 67,69 is fully engaged.

Thus when the first and third gears 67,79 are fully meshed, the second and fourth gears 69,81 are not meshed and when the third and fourth gears 69,81 are fully meshed, the first and third gears 67,79 are not meshed. The double pulse gear system ensures uninterrupted synchronised drive of the rotor assembly 5 and piston receiving wheel 7 at varying speeds during each revolution.

The operation of the pump 1 will now be described. The following description of the operation of the pump 1 is applicable to pumps 1 whether or not they include the synchronisation gear sets 63,65 as described above.

The inlet opening 9 of the pump is connected to an incoming fluid supply line (not shown) and the outlet 11 of the pump 1 is connected to an outgoing fluid supply line (not shown). When the pump is switched on by actuating the drive source the rotor assembly 5 begins to rotate and the piston element 21 that is currently located in the piston receiving recess 27 creates a partial vacuum as the piston element 21 withdraws from the piston receiving recess 27 thereby drawing fluid into the pump 1 through the inlet 9, and via the first slot 39 into the adjacent piston recess 27 and the interior of the pump via the passages 33,35. The pump is essentially self-priming in that the suction force created is sufficiently large to flood the piston receiving recess 27 and at least part of the low pressure side 61. The fluid is sucked towards the rotor assembly 5 tangentially in a manner that is substantially in the direction of rotation of the rotor assembly. The fluid is pushed around the inner periphery 57 of the casing by the piston elements 21 and is delivered to the outlet 11 by the piston elements pushing fluid through the passageways 33,35 on the high pressure side 59. The fluid flows through the second slot 41 in the splitter element 13 and out of the outlet 11. As shown in FIG. 5, the fluid is initially pushed through one of the passageways 35 until the next piston receiving recess 27 rotates into a position where it is able to receive fluid and the following piston element 21. The piston element 21 moves into the piston receiving recess 27 and expels any fluid therein through the passageway 33.

The pump 1 is fully reversible in that the present inlet 9 can become the outlet 11 and the present outlet 11 can become the inlet 9 simply by reversing the direction of operation of the drive source. This is due to the symmetry of the pump. It should be noted that gear pumps cannot do this since the seals in them are arranged in a directional fashion. If the user of the gear pump wants to reverse the direction, it is necessary to strip the gear pump down and reset the seals to enable flow in the opposite direction. This is not the case for the current pump 1. This is a significant advantage over standard gear pumps.

It has been found by the inventors that the pump described above has significant advantages over known gear pumps. In particular a greater volume of liquid can be moved for a particular operating speed and a greater suction can be produced. With regards to known piston pumps, there is a reduced pulsing of flow and a less complex arrangement

FIGS. 10 and 11 show an alternative arrangement to the piston receiving wheel 7 shown in FIGS. 1-7. The piston receiving wheel 107 includes passages 133,135 having a substantially square cross-section. The piston receiving wheel 107 would be manufactured as an integral structure in practice however in FIGS. 10 and 11 it is shown to be made up of outer layers 108,110 and a middle layer 112 that is sandwiched between the first and second outer layers 108,110, such that in FIG. 11 the outer layers 108,110 are removed so that an unobstructed view of the passage ways 133,135 can be achieved.

FIG. 12 shows a second embodiment of the invention. The embodiment shown comprises a pump 201 having a casing 203, first and second piston rotor assemblies 205, a piston receiving wheel 207, first and second fluid inlets 209 and first and second fluid outlets 211 in a splitter element 213. Each rotor assembly 205 has its own fluid inlet 209 and its own fluid outlet 211 similar to the first embodiment, and each rotor assembly 205 generates a low pressure side 261 and high pressure side 259 similar to the first embodiment. The splitter element 113 includes four apertures formed in the curved surface, one aperture connecting each of the inlets 109 (similar to the apertures 39 in FIGS. 6 and 7) and one aperture for each of the outlets 111 (similar to the outlets 41 in FIGS. 6 and 7). Optionally, the splitter element 313 can include seals located in each dividing wall, similar to seals 45 in dividing wall 43 shown in FIG. 7.

The advantage of having a second rotor assembly is that two separate circuits can be supplied by the pump 201 or alternatively the outputs can be combined to feed the same circuit. If the same circuit is supplied, having two smaller piston rotors as shown on a 1:2 nominal ratio can pump a greater volume of liquid than a single piston rotor having the same sized piston elements but having a 1:1 ratio (i.e. twelve piston elements).

FIG. 13 shows a third embodiment of the invention, that comprises a pump 301 having three piston rotor assemblies evenly distributed around a piston receiving wheel 307, that is the angle subtended between the centre lines of each of the piston rotor assemblies is approximately 120°. The nominal ratio between each piston assembly 305 and the piston receiving wheel 307 is 1:2. Each rotor assembly 305 includes its own fluid inlet 309 and fluid outlet 311 formed in a splitter element 313. In this arrangement up to three separate circuits can be supplied by the pump, or alternatively an increased volume of fluid can be moved by the pump 301 to one or two circuits. Each of the rotor assemblies 305 operates on a similar principle to the first embodiment thus producing a low pressure area 361 that sucks fluid in from the inlet 309 and a high pressure area 359 which forces the fluid out of the outlet 311.

The splitter element 313 includes six apertures in its curved surface. The arrangement is such that each inlet 309 is in fluid communication with one of the apertures (similar to slot 39 in FIGS. 6 and 7) and each of the fluid outlets 311 is in fluid communication with one of the apertures (similar to slot 41 in FIGS. 6 and 7). Thus each inlet 309 and each outlet 311 is in fluid communication with its own separate aperture. Optionally, the splitter element 313 can include seals located in each dividing wall (similar to seals 45 in dividing wall 43 shown in FIG. 7).

A fourth embodiment is shown in FIG. 14, which comprises a pump 401 having three piston rotor assemblies 405 evenly distributed about the piston receiving wheel 407. The nominal ratio between each rotor assembly 405 and piston receiving wheel 407 is 1:1. The pump 401 includes a splitter element 413 having one inlet port 409 and one outlet port 411. The splitter element 413 also includes three first apertures (not shown) in the curved wall of the splitter element 413 that are in fluid communication with each other and the inlets 409. The splitter element 413 also includes three outlet apertures formed in its curved surface that are in fluid connection with each other and the outlet 411. The arrangement is such that from a single inlet 409 each of the rotor assemblies 405 can be supplied with fluid along the fluid pathway 410. Similarly, fluid is taken away from each of the piston rotor assemblies 405 at a single outlet 411 via the fluid path 412. The inlet fluid path 410 and the outlet fluid path 412 are not connected and thus the inlet/outlet fluid remain separate from each other.

It will be appreciated, by the skilled person that modifications can be made to the above embodiments that are within the scope of the invention, for example a pump having any practical number of rotor assemblies can be included, for example between one and eight rotor assemblies, preferably one to four and more preferably still, one to three.

The nominal ratio between the or each rotor assembly and the piston receiving wheel can be adjusted to suit the application. For example, the nominal ratio can be 1:1, 1:2, 1:3, 2:1, 3:1, etc. The number of piston elements 21 and piston receiving recesses 27 can be increased or decreased as required.

For embodiments having a plurality of rotor assemblies, each rotor assembly can have its own first gear pair that is arranged to rotate about the second gear pair. For example, for the third and fourth embodiments, which include three rotor assemblies, the gear set includes three “first gear pairs”, one coupled with each rotor assembly, and one second gear pair, which is coupled with the piston receiving wheel. The pump can be driven by coupling one of the drive shafts to a drive source or alternatively mounting the piston receiving wheel and the second gear pair onto a drive shaft and coupling that drive shaft to the drive source. Using gears when there are multiple rotor assemblies is desirable since it spreads the drive load.

Whenever there is an arrangement having sufficiently few piston elements such that the piston receiving wheel 7 is fully disengaged by the rotor assembly, gears such as those shown in FIGS. 8 a-8 k can be used in order to synchronise the operation of the rotor assembly and the piston receiving wheel 7.

The splitter element 413 can be adapted to for use in the second and third embodiments, for example by reducing the number of apertures formed in the curved surface of the splitter element.

A fifth embodiment is shown in FIG. 15. The fifth embodiment is similar to the embodiments described above in that it includes a rotor assembly 505, however instead of having axial inlet and outlets, the inlet 509 and outlet 511 are arranged substantially radially towards the rotor assembly 5. Furthermore, the piston receiving wheel 507 does not include passageways similar to passageways 33,35 shown in FIG. 3. Instead, the function of the piston receiving wheel is to block fluid moving from a high pressure outlet side 559 to a low pressure input side 561. The interaction between the rotor assembly 505 and the piston receiving wheel 507 causes the piston receiving wheel 507 to rotate such that its peripheral portions engage with the piston support member 517 thereby blocking the flow of fluid from the high pressure side 559 to the low pressure side 561. Thus the only fluid pathway for the fluid is from the high pressure side 569 through the outlet 511. This is a simplified version of the invention compared with the embodiments described above. Since the number of piston elements 521 is small, the piston rotor 505 fully disengages the piston receiving wheel 507 while rotating and therefore it is necessary to synchronise the rotation of the piston receiving wheel 7 and the rotor assembly 505 with gears. It is to be noted that in this arrangement that conventional spur gears can be used for this purpose. This is because the interaction between the rotor assembly and the piston receiving wheel provides constant rotational speed. This is due to the piston chambers 527 having tapered sides therefore providing a less restricted interaction between the piston receiving wheel 507 and the piston elements 21. Since the rotor assembly 505 rotates substantially at a constant speed through a full 360° revolution the gears do not need to be of the type disclosed in FIGS. 8 a-8 k.

It will be appreciated by the skilled person that each of the above-embodiments can operate as fluid motors when fluid is supplied to the inlet under pressure. Useful work can be obtained from the motor, for example via the drive shaft. 

1. A rotary mechanism arranged to propel fluid and/or to be driven by a fluid, said rotary mechanism including: a rotor assembly having a plurality of piston members distributed about its periphery; a rotary member in peripheral engagement with the rotor assembly, said rotary member having a plurality of piston receiving formations in its periphery for receiving the piston members, the arrangement being such that during rotation of the rotor assembly the piston members move into and out of the piston receiving formations, and a plurality of conduits arranged to connect peripheral portions of the rotary member to an interior portion thereof; a flow separation device including an inlet port for receiving fluid into the rotary mechanism and an outlet port for enabling fluid to exit the rotary mechanism, a first passageway for connecting the inlet port with the interior side of at least one of the conduits formed in the rotary member and a second passageway for connecting the outlet port with the interior side of at least one of the conduits formed in the rotary member wherein the arrangement is such that, in use, the action of withdrawing the piston members from the piston receiving formations draws fluid into the rotary mechanism from the fluid inlet; and wherein the rotary member is rotatable relative to the flow separation device and at least some of the rotary member conduits periodically align with the first and second passageways formed in the flow separation device thereby enabling the fluid received from the inlet to flow outwards towards a first peripheral portion of the rotary member, wherein it is transported to a second peripheral portion of the rotary member by the rotor assembly, and for the fluid to flow away from the second peripheral portion of the rotary member to the outlet port, wherein the flow separation device is constructed and arranged to separate the incoming and outgoing flows.
 2. A rotary mechanism according to claim 1, wherein the input port is arranged substantially parallel to the axis of the rotary member and/or rotor assembly.
 3. A rotary mechanism according to claim 1, wherein the output port is arranged substantially parallel to the axis of the rotary member and/or rotor assembly.
 4. A rotary mechanism according to claim 1, wherein the flow separation device is arranged to direct the incoming fluid towards the rotor assembly such that the incoming fluid impinges on the rotor assembly in a substantially tangential direction in the direction of rotation of the rotor assembly.
 5. A rotary mechanism according claim 1, wherein the piston receiving formations are substantially U-shaped.
 6. A rotary mechanism according claim 1, wherein the piston receiving formations include at least one pair of substantially parallel sides.
 7. A rotary mechanism according to claim 1, wherein each piston comprises a body having a substantially cylindrical or substantially spherical portion.
 8. A rotary mechanism according to claim 1, wherein the geometry of the piston members and the piston receiving formations is such that interaction between pistons and the piston receiving formations periodically accelerates and decelerates the rotary member.
 9. A rotary mechanism according to claim 1, wherein the rotor assembly includes 1 to 20 piston members.
 10. A rotary mechanism according to claim 1, wherein the nominal ratio between the number of piston members and the number of piston receiving formations in the range is 4:1 to 1:4.
 11. A rotary mechanism according to claim 1, wherein the rotor assembly includes a support member for supporting each of the piston members, the arrangement being such that the piston members are located about the periphery of the support member and are arranged to rotate with the support member about a first axis, wherein at least one of the piston members is arranged to rotate relative to the support member about a second axis.
 12. A rotary mechanism according to claim 1, including a plurality of rotor assemblies in peripheral engagement with the rotary member.
 13. A rotary mechanism according to claim 1, wherein the flow separation device includes a plurality of inlet ports and/or a plurality of outlet ports.
 14. A rotary mechanism according to claim 1, wherein the flow separation device includes at least one inlet port and/or one outlet port that is connected to a plurality of apertures formed in the flow separation device that are arranged to communicate with the rotary member conduits.
 15. A rotary mechanism according to claim 1, including a gear set for synchronising the rotation of the rotor assembly and the rotary member.
 16. A rotary mechanism according to claim 15, wherein said gear set includes a first gear pair comprising first and second gear elements, wherein each of said first and second gear elements includes meshing zones and non-meshing zones formed in its periphery and the first gear element is arranged to rotate with the second gear element; and a second gear pair including third and fourth gear elements, wherein each of the third and fourth gears elements includes a plurality of meshing zones and non-meshing zones formed in its periphery and the third gear element is arranged to rotate with the fourth gear element; wherein the first and second gear pairs are in meshing engagement such that the first gear element meshes with the third gear element and the second gear element meshes with the fourth gear element, and drive between the first and second gear pairs is transmitted alternately between the first and third gears and the second and fourth gears.
 17. A rotary mechanism according to claim 16, wherein for each of the first and second gear elements, the non-meshing zones are arranged alternately with the meshing zones, the first and second gear elements are arranged substantially co-axially such that the meshing zones of the first gear element are rotationally offset from the meshing zones of the second gear element.
 18. A rotary mechanism according to claim 17, wherein each of the first and second gear elements includes a central portion and a plurality of lobes distributed around the periphery of the central portion, wherein each lobe includes a peripheral portion having meshing means formed therein.
 19. A rotary mechanism according to claim 18, wherein the periphery of each lobe is substantially part elliptical.
 20. A rotary mechanism according to claim 16, wherein for each of the third and fourth gear elements the non-meshing zones are arranged alternately with the meshing zones, the third and fourth gear elements are arranged substantially co-axially such that the meshing zones of the third gear element are rotationally offset from the meshing zones of the fourth gear element.
 21. A rotary mechanism according to claim 20, wherein each of the third and fourth gear elements includes concave portions formed in its periphery, wherein alternate concave portions including meshing means formed therein.
 22. A rotary mechanism according to claim 21, wherein the concave portions are substantially part elliptical.
 23. A rotary mechanism according to claim 16, wherein the meshing means include involute gear teeth.
 24. A rotary mechanism according to claim 16, wherein maximum acceleration occurs at the handover of meshing engagement from at least one of the first and third gear elements to the second and fourth gear elements and from the second and fourth gear elements to the first and third gear elements.
 25. A rotary mechanism according to claim 16, wherein the minimum speed occurs at the handover of meshing engagement from at least one of the first and third gear elements to the second and fourth gear elements and from the second and fourth gear elements to the first and third gear elements.
 26. A rotary mechanism according to claim 16, wherein the maximum speed occurs when either the first or second gear element pair is fully engaged.
 27. A rotary mechanism according to claim 16, wherein the first and second gear pairs are arranged such that the second gear element meshes with the fourth gear element before the first gear element fully disengages the third gear element. 28-49. (canceled) 